What the LDR service is

Hosted by each Storage Node, the Local Distribution Router (LDR) service handles content transport for the StorageGRID system. Content transport encompasses many tasks including data storage, routing, and request handling. The LDR service does the majority of the StorageGRID system’s hard work by handling data transfer loads and data traffic functions.

The LDR service handles the following tasks:

The LDR service also manages the mapping of S3 and Swift objects to the unique “content handles” (UUIDs) that the StorageGRID system assigns to each ingested object.

Queries

LDR queries include queries for object location during retrieve and archive operations. You can identify the average time that it takes to run a query, the total number of successful queries, and the total number of queries that failed because of a timeout issue.

You can review query information to monitor the health of the metadata store, which impacts the system’s ingest and retrieval performance. For example, if the latency for an average query is slow and the number of failed queries due to timeouts is high, the metadata store might be encountering a higher load or performing another operation.

You can also view the total number of queries that failed because of consistency failures. Consistency level failures result from an insufficient number of available metadata stores at the time a query is performed through the specific LDR service.

You can use the Diagnostics page to obtain additional information on the current state of your grid. See the information on monitoring and troubleshooting StorageGRID.

Monitoring and troubleshooting StorageGRID

ILM activity

Information lifecycle management (ILM) metrics allow you to monitor the rate at which objects are evaluated for ILM implementation. You can view these metrics on the Dashboard or on the Nodes page > ILM tab for each Storage Node.

Object stores

The underlying data storage of an LDR service is divided into a fixed number of object stores (also known as storage volumes). Each object store is a separate mount point.

You can see the object stores for a Storage Node on the Nodes page > Storage tab.


Object stores

The object stores in a Storage Node are identified by a hexadecimal number from 0000 to 002F, which is known as the volume ID. Space is reserved in the first object store (volume 0) for object metadata in a Cassandra database; any remaining space on that volume is used for object data. All other object stores are used exclusively for object data, which includes replicated copies and erasure-coded fragments.

To ensure even space usage for replicated copies, object data for a given object is stored to one object store based on available storage space. When one or more object stores fill to capacity, the remaining object stores continue to store objects until there is no more room on the Storage Node.

Metadata protection

Object metadata is information related to or a description of an object; for example, object modification time, or storage location. StorageGRID stores object metadata in a Cassandra database, which interfaces with the LDR service.

To ensure redundancy and thus protection against loss, three copies of object metadata are maintained at each site. The copies are evenly distributed across all Storage Nodes at each site. This replication is non-configurable and performed automatically.

Managing object metadata storage